Final Contour Ripping and Air-SeedingFollowing the return of overburden and topsoil the pit is ripped to a minimum depth of 0.8 m on contour by a dozer fitted with three tines. Ripping is undertaken on contour, that is along lines with the same elevation, to increase the soil’s water storage capacity. Mounds created by the contour ripping also stops soil erosion. The minimum depth of 0.8 m is deep enough to alleviate the re-compaction caused by the soil return operation. The pre-ripping operation, which is carried out after landscaping to a minimum depth of 1.5 m allows deep root growth and water infiltration.

Seed is applied immediately onto the freshly ripped ground by a computer controlled air-seeder machine mounted on the contour ripping dozer. Research has shown that the timing of the applied seeding is important and ripping in dry soil conditions between December and April optimises plant establishment. Ripping in the dry season also allows good establishment of plants from the natural soil seedbank which otherwise be destroyed if the ripping was carried out in winter. Dry season ripping also prevents dieback spread from wet soil, produces a better soil structure and avoids large machines being bogged in wet soil.

The introduction of mechanical seeding by the dozer was a major improvement in the seeding process - not only replacing the strenuous work of handseeding, but also seed is broadcast directly onto freshly ripped ground. A feature of the air-seeder is its ability to handle mixed seed from the jarrah forest of varied size and shape. It can deliver very small amounts of seed. The seed application rate is as low as 1.1 - 1.5 kg per hectare. Such low seed rates are achieved by seed moving from a seed bin through a chute onto the face of a slowly turning sponge which turns and drops the seeds into the delivery chute. The speed of the turning sponge is controlled by the speed of the dozer. When the dozer stops the seed delivery stops. Larger zamia seeds are applied by hand.

Click image to enlarge.The air seeder blows seed out of the two pipes from the back of the dozer during the final contour ripping with a multitine.